There are many different structural materials, made at least in part from synthetic resins, that are intended to be used in place of wood. An elusive goal in designing such materials is the combination of reasonable cost with relatively high strength and stiffness. Thus, for example, synthetic lumber made by hot-melt extrusion of mixtures of waste wood fiber and recycled thermoplastic material such as polyethylene can be produced at a low enough cost to make them feasible for use as decking boards. Such synthetic lumber is generally considered unsuitable, however, for uses that require it to withstand higher bending and compression loads, require increased static strength and stiffness requirements, and/or require greater shock and impact resistance. Thus, it is generally unsuitable for use as primary structural load-bearing elements, such as posts, joists, beams, and stringers for shipping pallets. For those types of uses a material has to have a higher flexural modulus of rupture, izod impact resistance, ultimate compressive strength, Young's modulus, and/or accelerating weight resistance than are found in the hot-melt extrudates of polymer and wood particles.